Surgical resection of epileptogenic foci is a commonly practiced and often beneficial treatment for patients suffering debilitating seizures arising from otherwise intractable epilepsy. The success of this procedure depends on the ability of the medical team to precisely locate the epileptogenic zones in the patient's brain and to identify important cortical regions that must be avoided during resection. The accepted best method for locating the epileptogenic zones is to record seizure activity with subdural electrodes implanted chronically for up to seven days. The electrodes are connected by cables to external recording equipment for the duration of the monitoring period. This invasive procedure has disadvantages: (a) A lengthy and costly hospital stay is required. (b) Long-duration implantations increase the likelihood of serious and potentially lethal infection. (c) A family member or sitter must be with the patient at all times. (d) Being in bed and tethered to the wall by numerous cables makes it difficult for some patients to cope. (e) There is a risk of intracerebral hemorrhage if the cables are accidentally pulled and the grids move. (f) Ten to twenty percent of patients do not have enough seizures during the hospitalization period to identify the epileptic zone with certainty. We propose to develop wireless subdural electrodes that will avoid these disadvantages. Wireless electrodes will allow complete closure of the craniotomy used for surgical placement and will avoid the use of the transcranial multiwire cables that connect the electrodes to data processing hardware. The ability to close the dura and skull, avoiding wired conduits to the brain, will reduce the risk of morbidity due to infection and reduce cost by allowing the patient to leave the hospital for the majority of the monitoring phase. A potentially significant benefit of wireless outpatient monitoring is the ability to provide longer monitoring periods, up to 29 days, which allows the recording of habitual seizure activity while the patient is on their full regimen of ant-seizure medication. Localization based on habitual seizure activity will improve outcomes of the resective surgery and expand the population of patients for whom surgery is an option. The Phase II objective is to establish the diagnostic capabilities and safety of wireless devices over 29-day implantation period in dog using a side-by-side comparison to clinical, hardwired subdural grids and recording systems as a basis for the assessment. Program success is defined as achieving clinically equivalent seizure localization data to conventional grids and equivalent or reduced pathology. These data will serve as the basis for an IDE application for a safety and efficacy study in patients under the direction of our clinical collaborators at the University of Chicago. The Phase II Aims are as follows: Aim 1. To develop wireless ECoG devices for functional and safety testing in dog. Aim 2. To design and test external hardware and software for dog studies. Aim 3. To evaluate wireless ECoG device function and stability over 29 days in dog. Aim 4. To evaluate biocompatibility and safety of 29 day implants in dog. The Phase II program is a collaboration between EIC Laboratories (Norwood, MA), Sigenics (Chicago, IL), Illinois Institute of Technology (Chicago, IL), and the University of Chicago. Array fabrication and testing will be conducted at EIC. ASIC design and procurement will be managed by Sigenics. IIT will oversee the telemetry system and electrical interface development. Animal studies will be conducted at the University of Chicago. We estimate the market for wireless devices used in intracranial monitoring for resective epilepsy surgery will be $12-19M annually in the United States. Expansion of the market to include other clinical monitoring applications and devices that provide stimulation-based therapies will be sought. A modest market for research devices is also anticipated.